1. Field of the Invention
The present invention relates to a speech recognition apparatus and method.
2. Related Art
A conventional speech recognition apparatus and method used as a man-machine interface analyzes a speech signal received via a microphone and extracts characteristic parameters from the speech signal. The characteristic parameters are compared with reference patterns in a vocabulary stored in a dictionary section of the apparatus, and one or more words corresponding to the reference patterns which have high similarities with the extracted characteristic parameters are selected and outputted. The apparatus generally selects and outputs at least a word even if no reference pattern in the vocabulary has a high similarity with the characteristic parameters. In this case, the speech signal is often misrecognized. Further the speech signal is often misrecognized due to the background noise. If the result of the misrecognition is used for controlling an external device, the operation of the external device may be adversely and seriously affected.
For example, the speech recognition apparatus is used for a car navigation device which has a voice-control function for receiving a speech as an input control signal and outputting a speech as a query to a user or a reply to the user's query. If the user says ‘shukushou’ which means ‘reduce’ so that the map is reduced, it may be misrecognized as ‘jitaku’ which means the user's house. In this case, the apparatus discards the route to the destination and newly searches a route to the user's house, if the apparatus is configured to execute a command immediately in response to the input speech signal. In this way, the route to the destination is discarded against the user's will.
If the apparatus is configured to confirm the user's will, it queries ‘Your house will be set as the destination. OK?’, for example. If the user says ‘iie’ which means ‘NO’ as a reply to the query, the apparatus shifts to a wait state without searching a route to the user's house. However, the apparatus may misrecognize a user's reply as ‘hai’ which means ‘YES’, if the user says ‘shukushou’ again as a reply to the query by mistake. In this case, the route to the destination is also discarded.
In this way, the external device may operate against the user's will, if the speech signal from the user is misrecognized as a specific word such as ‘hai’ included in the vocabulary. Therefore, it is preferable that the speech recognition apparatus employs a technique for preventing the external device from performing an erroneous operation, which cannot be easily undone, against the user's will in response to the result of misrecognition.